1. Field of the Invention
The present invention relates to a method for fabricating copper/indium/gallium/selenium (CIGS) nanoparticles, and more particularly, to a wet ball mill method using zirconia beads.
2. The Prior Arts
Nanoparticles generally means particle with size smaller than 100 nm, and the transition from microparticles to nanoparticles can lead to a number of changes in, such as optical, thermal, magnetic and mechanical properties.
When gold is split into the particle with size smaller than the wavelength of light, gold loses the originally wealthy luster and renders black for its special optical properties. For examples, silvery-white platinum becomes black platinum black in the nano size and golden chromium becomes black chromium in the nano size. Actually, all the metal render black in the nanoparticle size and the color becomes blacker with smaller size. Therefore, nanoparticles have lower reflectivity and higher light absorbance.
Under the global consciousness of green and environmental protection to save power consumption and reduce carbon dioxide emission, CIGS solar cell has no material shortage problem as the silicon solar cell depends on silicon wafer excessively, and also no high material cost problem as dye-sensitized solar cell (DSSC) requires the photosensitized dyes. In addition, the optimal photoelectric conversion efficiency of CIGS solar cell can achieve to 25%, and the photoelectric conversion efficiency of flexible plastic substrate has achieved to 14% such that CIGS solar cells possess a high development potential for the future.
The CIGS solar cell generally comprises an absorption layer as a p-type layer and a zinc sulfide (ZnS) layer as a n-type layer, wherein the absorption layer is the copper indium gallium diselenide (Cu(In,Ga)Se2) layer and the light-absorption efficiency of the absorption layer influences the photoelectric conversion efficiency of CIGS solar cell directly.
Recently, a lot of methods for fabricating CIGS nanoparticles was brought out for preparing the absorption layer with high light absorbance, including physical methods and chemical methods, wherein the physical methods comprise vapor condensation, mechanic ball mill method, physical crumbling, thermal disintegrating and supercritical fluid, and the chemical methods comprise chemical vapor deposition, sol-gel, microemulsion, polymer graft, hydrothermal synthesis, arc plasma, and sonochemical methods. Mechanic ball mill method has better economy benefit so that mechanic ball mill method has development potential, especially to wet ball mill method which uses liquid as a mediator between milling ball and the materials-being-milled for increasing the milling efficiency.
The disadvantages of the prior arts are that the wet ball mill method needs to use the high energy and high precision apparatus, and the wet ball mill method is limited by the original particle size and the properties of individual materials-being-milled, and thereby the range of the particle sizes and homogeneity of CIGS particles can not be controlled precisely at one time and thus consumes a lot of energy. Accordingly, a multi-stage milling method is required. The multi-stage milling method is that the individual materials are first milled to produce the individual milled materials which have specific size and maintain their original physical properties and surface state, and then the different individual milled materials are homogeneously mixed together, and the size of milling ball is reduced step by step in the two-stage milling process so that the particle sizes of CIGS particles can be reduced to the desired range to eliminate the disadvantages of the prior arts.